tpm: vtpm_proxy: Prevent userspace from sending driver command

To prevent userspace from sending the TPM driver command to set
the locality, we need to check every command that is sent from
user space. To distinguish user space commands from internally
sent commands we introduce an additional state flag
STATE_DRIVER_COMMAND that is set while the driver sends this
command. Similar to the TPM 2 space commands we return an error
code when this command is detected.

Signed-off-by: Stefan Berger <[e-mail]>
Reviewed-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>

drivers/char/tpm/tpm_vtpm_proxy.c

···
 #define STATE_OPENED_FLAG        BIT(0)
 #define STATE_WAIT_RESPONSE_FLAG BIT(1)  /* waiting for emulator response */
 #define STATE_REGISTERED_FLAG	 BIT(2)
+#define STATE_DRIVER_COMMAND     BIT(3)  /* sending a driver specific command */
 
 	size_t req_len;              /* length of queued TPM request */
 	size_t resp_len;             /* length of queued TPM response */
···
 	return len;
 }
 
+static int vtpm_proxy_is_driver_command(struct tpm_chip *chip,
+					u8 *buf, size_t count)
+{
+	struct tpm_input_header *hdr = (struct tpm_input_header *)buf;
+
+	if (count < sizeof(struct tpm_input_header))
+		return 0;
+
+	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+		switch (be32_to_cpu(hdr->ordinal)) {
+		case TPM2_CC_SET_LOCALITY:
+			return 1;
+		}
+	} else {
+		switch (be32_to_cpu(hdr->ordinal)) {
+		case TPM_ORD_SET_LOCALITY:
+			return 1;
+		}
+	}
+	return 0;
+}
+
 /*
  * Called when core TPM driver forwards TPM requests to 'server side'.
  *
···
 			count, sizeof(proxy_dev->buffer));
 		return -EIO;
 	}
+
+	if (!(proxy_dev->state & STATE_DRIVER_COMMAND) &&
+	    vtpm_proxy_is_driver_command(chip, buf, count))
+		return -EFAULT;
 
 	mutex_lock(&proxy_dev->buf_lock);
 
···
 	struct tpm_buf buf;
 	int rc;
 	const struct tpm_output_header *header;
+	struct proxy_dev *proxy_dev = dev_get_drvdata(&chip->dev);
 
 	if (chip->flags & TPM_CHIP_FLAG_TPM2)
 		rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS,
···
 		return rc;
 	tpm_buf_append_u8(&buf, locality);
 
+	proxy_dev->state |= STATE_DRIVER_COMMAND;
+
 	rc = tpm_transmit_cmd(chip, NULL, buf.data, tpm_buf_length(&buf), 0,
 			      TPM_TRANSMIT_UNLOCKED | TPM_TRANSMIT_RAW,
 			      "attempting to set locality");
+
+	proxy_dev->state &= ~STATE_DRIVER_COMMAND;
+
 	if (rc < 0) {
 		locality = rc;
 		goto out;